Two stage process of refining diesel fuel



,. ICC

Patented Jan. 5, 1965 3,164,546 TWO STAGE PROCESS OF REFlNlNG DIESEL FUEL Allen F. Millikan, William L. Fierce, and Roger L. Weichman, all of Crystal Lake, Ill., assignors to The Pure Oil Company, Chicago, 111., a corporation of Ohio No Drawing. Filed Dec. 22, 1961, Ser. No. 161,374

' 13 Claims. (Cl. 208-236) This invention relates to new and useful improvements in processes for refining mineral oil fractions which contain a substantial quantity of sulfur compounds. This invention'is further concerned with a process for refining petrolcumfractions of the diesel-oil boilingrange to produce diesel fuels of'improved cetane number and odor, and includes a novel processing step for removing colored reaction products produced during a preliminary refining step.

Petroleum fractions, e.g., naphthas, kerosenes, .gasolines, fuel oils, diesel oils, lubricating oils, waxes, etc., as normally obtained from petroleum often have unsatisfactory odor characteristics resulting from the presence of malodorous mercaptans and other sulfur compounds. The removal of these malodorous constituents has oftenproved difficult by ordinary refining procedures. In the past,

removal of mercaptans has been accomplished to some extent by clay treating and by treatment with chemicals which form readily extractable derivatives. In some cases, the removal of mercaptans and other sulfur compounds has been impractical and the sour petroleum fractions have been treated by a sweetening process in which the sulfur compounds, such as rnercaptans, are converted to derivatives of lesser odor.

In the past, petroleum fractions have been treated with a varitey of chemicals to give products with improved odors. Naphthas have been treated with absorbents of various types and have been treated with various amines during distillation to prevent the formation of .malodorous constituents. Petroleum fractions have been subjected to solvent extraction with various acidic materials such as sulfur dioxide, phenol, and concentrated organic acids to extract color-forming and odor-forming constituents. In the copending patent application of William L. Fierce and Roger L. Weichman, Serial No. 137,028., filed September 11, 1961, now Patent No. 3,135,680, a process is described in which a sour diesel-fuel oil fraction is converted to a product having a good odor rating and improved cetane number by. treatment with gaseous nitrogen dioxide at a relatively low temperature, preferably in the range from about 0 to 40 C. The amount of nitrogen dioxide required is dependent upon the degree of cetane number improvement desired and the amount of sulfurcompounds in the sour oil. The product which is obtained upon treatment of the diesel fuel with nitrogen dioxide tends to have an objectionable color which develops during the nitrogen dioxide treatment. It has been possible to remove the color-forming ingredients by severe acid treatment or absorption, but the removal of the colored materials in the oil has generally resulted in a reduction in cetane number of the fuel oil.

It is therefore one object of this invention to provide a new and improved process for treating petroleum fractions of the diesel-oil boiling range to increase cetane number, eliminate mercaptans, and improve odor characteristics.

A feature of this invention is the provision of a process in which a sour petroleum fraction of the diesel-oil boiling range is treated with gaseous nitrogen dioxide at a relatively low temperature, and then washed with water to remove water-soluble products.

Another feature of this invention is the provision of a process in which a sour petroleum fraction is washed with aqueous caustic and treated with gaseous nitrogen dioxide at a relatively low temperature, and then washed with Water to produce a petroleum product of improved odor and cetane number and a satisfactory corrosion rating as measured by the ASTM copper-strip corrosion test.

Still another feature of this invention is the provision of a process in which a petroleum fraction is treated with gaseous nitrogen dioxide at a relatively low temperature, and subjected to washing with aqueous caustic and/or solvent extraction with a solvent selected from the group consisting of nitromethane, dimethylformamide, pyridine, acetonitrile, glycolonitrile, ethylene glycol, ethanolamine, and phenol, to remove colored reaction products and thus obtain a product of improved odor and cetane number and reduced sulfur content and color.

Other objects and features of this invention will become apparent from time to time throughout the specification and claims as hereinafter related.

In the aforementioned copending patent application of Pierce and Weichman, a process is described in which a sour petroleum fraction of the diesel-oil boiling range is treated with gaseous nitrogen dioxide at a temperature of about 0-40 C. which converts malodorous mercaptans into substantially odorless reaction products. This treatment is also effective to increase the cetane number of the fuel oil. It was found, however, that the nitrogen dioxide treatment of diesel-fuel oils also results in the formation .of dark-colored reaction products which give an objectionable color to the fuel oil. Numerous methods have been tried to remove these colored reaction products, but in most cases the removal of the colored reaction products results in a decrease in cetane number of the fuel oil. In accordance with this invention, we have found that a diesel-fuel oil which has been treated with nitrogen dioxide at 0-40 C. and has acquired an objectionable color can be converted to a product having a satisfactory color without loss of cetane number of the fuel by subjecting the 'nitrogen-dioxide-treated oil to solvent extraction with a solvent selected from the group consisting of nitromethane, 'dimethylformamide, pyridine, acetonitrile, glycolonitrile, ethylene glycol, ethauolarnine, and phenol. This solvent extraction may be accompanied by a caustic wash, .Or the solvent may be mixed with aqueous caustic to produce a further improvement in color, odor, and corrosion properties of the oil.

In measuring therelative odor of petroleum products, it is not possible to develop a precise quantitative measure of odor which is entirely independent of the individual who evaluates the odor. Nevertheless, there are certain procedures for rating odors which have been used in the petroleum industry. Odor evaluation standards and methods have been proposed by a joint committee of the ASTM and TAPPI. A modification of this procedure has been used extensively in the evaluation of the odor of commercial petroleum products. In a typical petroleum company, an odor panel is selected consisting of several, e.g., 10 to 20 or more, individuals who have been tested for their ability to discriminate between and match different odors. One test for selection of panel members involves correctly matching a series of chemical odors such as very dilute odors of acetic acid, phenol, toluene, and benzene. A second test involves a matching of a variety of different naphthas by odor from a single manufacturing source. A third test involves the matching of mineral spirits obtained from .diiferent manufacturers. By use of these screening tests it is possible to select a panel of 10 to 29 individuals who are especially discriminating in evaluating odors of petroleum products. In the rating of odors of petroleum fractions such as an odorless naphtha, a numerical rating scale has been established to describe odor quality:

Numerical Rating Odor Quality Excellent.

0. Very Good. Do.

Good. Fair (Just Passing). Borderline. Do. Poor. Very Poor.

When evaluating the odor of petroleum naphthas, the following procedure is used. The members of the odor panel are requested to avoid contact with contaminating odors, e.g., smoking, etc., for at least /2 hour prior to the test. The odor evaluation is carried out in an airconditioned room, at about 75 E, which is as free as possible from extraneous odors. Each member of the test panel rates the odor of a product separately. A nonmember of a panel conducts the test and is present to record any pertinent comments made regarding the odor. To eliminate bias, the product samples are coded, and the panel members are told only the type of product being rated. To avoid odor fatigue, no more than three samples are rated at any one time. Any additional ratings are spaced by at least three hours. A-total of seven panel members rate the product and the average of these opinions is reported as the odor rating.

In preparing the naphtha for odor evaluation, a 35-ml.

representative portion is poured into a clean, odor-free,

eight-ounce French square bottle. The bottle is sealed with a clean, odor-free, screw-on cap. The same sample is used by all members of the panel. The type bottle used in the evaluation is the same as used in the screening tests for selection of the panel member. The panel member evaluates the odor of the naphtha by removing the cap from the bottle, placing his nose at the bottle mouth and sniffing the odor. He checks the intensity of odor andrfor any foreign or undesirable odor that may be present and then numerically rates the odor using the above-described scale. This method is called the Wetodor of the naphtha.

In carrying out this invention, we have found that it is possible to convert sour diesel-fuel fractions to products having very good odor ratings and which are substantially improved in cetane number. Our process for deodorizing diesel fuels and improving the cetane number thereof consists essentially of two steps. First, the oil is treated with gaseous nitrogen dioxide at a relatively low temperature, preferably in the range from about to 40 C. The amount of nitrogen dioxide required is dependent upon the degree of cetane number improvement desired. The product which is obtained upon treatment of the diesel fuel with nitrogen dioxide ranges in color from yellow to dark orange. Secondly, the treated oil is washed with water until all water-soluble acidic material is removed. The final product is a clear diesel fuel oil having a color essentially the same as the product obtained in the first step. The oil can be dried before use if necessary. In some cases, the product obtained by this treatment is excessively corrosive, as measured by the Copper-Strip, Corrosion Test (ASTM Method D-130) In such cases, the product can be converted to one having a satisfactory corrosion rating by washing with aqueous alkali (NaOH, KOH, NH OH, etc.) before and/or after treatment with nitrogen dioxide, but prior to the final wash step.

The mechanism by which this process operates to remove sulfur compounds and to improve the cetane number of diesel-fuel oils is not known with certainty. It is known that nitrogen dioxide will react with a variety of organic compounds and sulfur compounds to form oxidation products which may or may not contain nitrogen. The nitrogen dioxide-treated diesel fuels obtained by our process probably contain reaction products of nitrogen dioxide with various components of the fuel oil since the nitrogen dioxide is taken up quantitatively by the oil and no nitrogen oxide by-products are given oif. However, the effect of these reaction products on cetane number and on odor is not disclosed in the prior art other than the aforementioned Fierce et a1. patent application. The increase in cetane number is also obtained when this treatment is given to fuel oils having a low sulfur content. The increase in cetane number may be due to the presence of compounds such as nitrates, nitrites, sulfoxides, and sulfones, but the presence of these compounds has not been established and it is not known with certainty just what causes the increased cetane number of the fuel. However, regardless of the identity of the reaction products and the mechanisms of the reactions involved, the result of our process is the formation of a diesel fuel oil with improved odor and substantially improved cetane number.

We have found that this process is generally applicable to mineral oil fractions boiling in the diesel-fuel boiling range, e.g., 177 to 330 C. The process is not applicable to the treatment of light petroleum distillates inasmuch as the color of the product and the increase in cetane number are objectionable properties in naphthas and gasolines. The treatment with nitrogen dioxide is carried out by bubbling gaseous nitrogen dioxide, either with or without an inert diluent gas, through the diesel fuel-oil at a relatively low temperature, preferably about 040 C. The nitrogen dioxide is added to the sour diesel oil in an amount sufficient to convert the malodorous sulfur compounds to odor-free products and improve the cetane number of the product. The nitrogen dioxide is used in an amount not less than the stoichiornetric amount required to react with substantially all of the sulfur compounds in the diesel fuel-oil, and larger proportions of nitrogen dioxide may be used if desired. When relatively small amounts of nitrogen dioxide are reacted with a sour diesel fuel-oil, all of the nitrogen content of the treating gas is retained in the oil in some form of chemical combination. The improvement in cetane number of the fuel is generally in proportion to the amount of nitrogen combined with the fuel oil in the nitrogen dioxide treatment. Water-washing of the treated fuel, or water-washing following a prior wash with aqueous caustic, is generally effective in producing a non-corrosive product.

During the nitrogen dioxide treatment of diesel-fuel oils, the oil develops a dark color which is objectionable in the case of diesel fuels. In some cases it is possible to remove the colored reaction products by certain fairly drastic color removal treatments. For example, the color may be removed by severe sulfuric acid treatment, by vacuum distillation of the oil away from the higher-boiling color products, or by adsorption (e.g., clay treating or treating with silica gel). In most cases, however, the separation of the oil from the colored reaction products produces a product which is sweet, but which has no higher cetane number than the oil prior to nitrogen dioxide treatment. The oil which is thus produced is useful as a furnace oil but has no particular advantage as a diesel fuel. In this process, we have found that the colored reaction products can be removed by extraction, following the nitrogen dioxide treatment, with a solvent selected from the group consisting of nitrometh-ane, dimethylformamide, pyridine, acetonitrile, glycolonitrile, ethylene glycol, ethanolamine, and phenol. The oil is preferably washed following the solvent extraction step to remove any dissolved solvent and then dried prior to use.

The following non-limiting examples are illustrative of the scope of this invention.

EXAMPLE I Untreated diesel-fuel oil, 1000 ml, is charged to a 3,000 ml. 3-necked flask equipped with a stirrer, thermometer,

and bubbler tube. The oil which is used is a refinery product known as untreated range oil and has the following distillation range: I.B.P. 178 C., 5%, 193 C., 50%, 232 C., 95%, 273C and RP. 288 C. The oil has a total sulfur content of about 0.53% wt., is rated sour by the doctor test, and has an odor rating of about 7. This oil is normally converted to a No. 1 furnace oil, also usable as a diesel fuel-oil, by doctor treatment. The oil which is treated in accordance with this invention has an initial cetane number of 48.7. The oil is maintained at about 5 C. by Dry Ice-acetone bath and nitrogen dioxide is bubbled in over a period of 100 minutes at a rate sufiicient to add 3.1 g. nitrogen dioxide to the oil. The resulting product is a slightly cloudy, medium-orange liquid. This treated fuel oil is then washed 5 times with 400-ml. portions of distilled water. The product is then dried by filtering through a double thickness of Reeve- Angel paper (filter paper used for removing entrained water). The product is a fairly dark, orange liquid which is doctor sweet and which has an odor rating of 4. The cetane number of the fuel has increased from an initial value of 48.7 to a treated value of 51.8. Thus, the addition of 3.1 g. nitrogen dioxide to 1000 ml. dieselfuel oil results in an increase of 3.1 in cetane number. The treated oil is reduced by about 25% total sulfur content by this treatment. The oil which is obtained by this treatment is doctor sweet, substantially improved in "odor, and appreciably improved in cetane number.

The diesel oil which is produced by the treatment has an ASTM color of about 7-8. This color is considered objectionable in diesel fuels. A 40-ml. portion of this fuel oil is shaken vigorously with ml. of dimethylformamide. The phases are separated and the raifinate (oil phase) is washed with water and dried by filtration through Reeve-Angel filter paper. The product which is obtained by this treatment has an ASTM color of about 3-4 and a cetane number of about 50.

EXAMPLE II Two liters of No. 2 fuel oil were treated with 7.6 g. of nitrogen dioxide (at a rate of 1.35 lbs. of nitrogen dioxide/ barrel of oil), and the treated material was filtered through a double thickness of Reeve-Angel paper to remove the by-product sludge. Then, onehalf the filtrate was set aside for later experiments and one-half was Washed five times with 400-ml. portions ofa mixture of 75% 0.4 N aqueous sodium hydroxide and acetone. The raflinate from this extraction was washed three times with water and driedby filtration through a double thickness of Reeve-Angel paper after which the ASTM color of the product was determined. The product at this point was foundto have an ASTM color rating of 6.

Next, a -ml. portion of the product was shaken vigorously with 20 ml. of dimethylformamide. The raffinate phase was recovered and the ASTM color rating determined to be 3 /2.

EXAMPLE III The second half of the initial filtrate from Example II Was Washed five times With 400-ml. portions of 0.4 N aqueous sodium hydroxide, and then was washed '3 times with water and dried by filtration through a double thickness of Reeve-Angel paper, to obtain a product having a cetane number of about 46 (cetane number of the fuel oil prior to N0 treatment was 41.2) and an ASTM color of 7. The fuel oil which was obtained by caustic and water washing was then divided into a number of 40-rnl. portions and treated with various solvents to determine the feasibility of removal of the colored reaction products without adversely affecting the cetane number of the fuel oil. In each case a 40-ml. portion of the causticand water-washed product Was shaken vigorously in a 100-ml. mixing graduate with 20 ml. of solvent. The phases were allowed to separate, the volume relation of the phase was measured, and the yield was computed from the recovered 6 volume of rafiinate. Finally, the ASTM color of each ratlinate phase was determined. The results of these measurements are set forth in Table I.

Table I Raffinate, Product Solvent percent ASTM Yield (By Color Volume) Dimethylforrnamide 93 -3% 98% Aqueous N itromethane 98 -4% Aqueous Pyridine 1 113 6 60% Aqueous Pyridine" 1 108 7 Acetonitrile 95 -4% Glycolonitrile- 6 Ethylene Glycol. 98 G Ethannlamine 100' 5 91% Aqueous Phenol 88 4 lhe 100% yields are accounted for by the unusual solubility of pyridine in the raifinate. This dissolved pyridine could be easily removed by water washing or distillation.

The fuel oil which was recovered in each of the several experiments in Table I was considerably improved in color and the cetane number of the fuel was not adversely affected. In fact, the fuel oil obtained by extraction with dimethylformamide has a slightly higher cetane number than the nitrogen dioxide treated oil which was not subjected to extraction.

EXAMPLE IV A No. 2 fuel oil, 2.9 liters, Was treated with nitrogen dioxide at about 40 C. at a rate of 1.17 lbs. nitrogen di dioxide per barrel of oil. The treated oil was filtered through a double thickness of Reeve-Angel paper to remove by-product sludge. The filtrate was designated as product N. Next, one liter of product N was extracted with four successive ZOO-ml. portions of a solvent com- Reeve-Angel paper, and the filtrate designated as product P. Products N, O, and P were evaluated for odor, color, cetane number, corrosivity, and efficiency of recovery. The results of these measurements are set forth in Table II.

Table II Product N O P Solvent None Per Oil Recovery 91. 5 91. 7 Percent Total sulfur... 0. 94 0. 74 0.77 Percent Mercaptan sulfur 0. 001 0v 001 0. 001 Percent Nitrogen 0.08 0. 02 0. 02 Odor 3 CopperStrip COXTOSlOH 1 la la Octane Num er 46 2 48.6 46.2 C or +4 1 Aqueous dimethylforrnamide. 2 Aqueous caustic+Diinethylformamide.

From these experiments it is seen that the treatment of a No. 2 diesel-fueloil resulted in an increase of about 5 units in the cetane number "of the fuel. The treated oil, howevenhad an objectionable color. The extraction of the treated oil with aqueous dimethylformamide resulted in a very substantial improvement in the color and a mild improvement in the odor of the treated fuel oil. This treatment actually resulted in a slight increase in the cetane number of the value attained as a result of the nitrogen dioxide treatment. The treatment with a mixture am ne 7 of aqueous causticand dimethylformamide resulted in a further improvement in the color, but gave a product which had the same-cetane number as the nitrogen dioxidetreated fuel oil. i 1

As a result of our experiments We have found that sour diesel-fuel oils can be rendered doctor sweet and improved in cetane number by treatment with nitrogen dioxide, followed by filtration, caustic washing, and water washing. .The product which is obtained, however, has an ObjCCtiOH! able color but can be rendered satisfactory with respect to color by extraction of the nitrogen-dioxide-treated oil with a solvent selected from the group consisting of nitromethane, dimethylformamide, pyridine, acctonitrile, glycolonitrile, ethyleneglycol, ethanolamine, and phenol. The extraction may be carried out using the solvent alone, or in admixture with Water, or with an aqueous solution of caustic (e.g., sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, etc.), and the treated oil may be given a subsequent caustic wash and water wash if desired. Where the oil has been washed after being subjected to solvent extraction it is usually desirable to dry it prior to use.

While we have described our invention fully and completely with special emphasis on several preferred embodi- V ments we wish it to be understood that within the scope of the appended claims this invention may be practiced otherwise than as specificallydescribed herein.

The embodiments of the invention in which an exclusive property or privilege is claimed are as follows:

1. In the treatment of fuel oils of the diesel-fuel boiling range by contacting the oil at 40 C. with sufficient nitrogen dioxide to improve the cetane number thereof, the improvement of (a) contacting the treated oil with a solvent selected from the group consisting of nitromethane, dimethylformamide, pyridine, acetonitrile, glycolonitrile, ethylene glycol, ethanolamine, and phenol; and obtaining a rafiinate phase predominating in said treated oil and (b) washing the resulting rafiinate phase with water to remove any dissolved solvent.

2. A method in accordance with claim 1 in which the oil is a sour petroleum fraction of the diesel-fuel boiling range having an appreciable initial mercaptan content and the nitrogen dioxide is contacted therewith in an amount not less than the stoichiometric amount required to react with the sulfur compounds therein.

3. A method in accordance with claim 2 in which the oil is washed with aqueous alkali prior to treatment with nitrogen dioxide. 7

4. A method in accordance with claim 2 in which the oil is washed with aqueous alkali after treatment with nitrogen dioxide.

5. A method in accordance with claim 2 in which a caustic wash accompanies the contacting of said treated oil with said solvent.

6. A method in accordance with claim 2 in which thetreated oil is filtered prior to contacting with said solvent.

7. A method in accordance with claim 2 in which the treated oil is dried after water-washing.

8. In the treatment of sour fuel oils of the diesel-fuel boiling range by contacting the oil at 040 C. with sufiicient nitrogen dioxide to react with the sulfur compounds therein and to improvethe cetane number thereof, the improvement of 1 (a) contacting the oil with dimethylformamide to re-,

6 move colored reaction products therein; obtaining a raiiinate phase predominating in said oil (b) washing the resulting raflinate phase with water to remove any dissolved solvent; and

(c) drying the treated oil.

9. A method in accordance with claim 8 in which said dimethylformamide is in admixture with an aqueous solution of caustic. v V

10. In the treatment of sour fuel oils of the diesel fuel boiling range by contacting the oil at 040 C. with sufficient nitrogen dioxide toreact with the sulfur compounds therein and to improve the cetane number thereof, the improvement of (a) contacting the oil with nitromethane to extract colored reaction products therein; and obtaining a raifinate phase predominating in said oil (b) washing the resulting rafiinate phase with Water to remove any dissolved solvents; and

(c) drying the treated oil.

11. In the treatment of sour fuel oils of the diesel-fuel boiling range by contacting the oil at 040 C. with sufiicient nitrogen dioxide to react with the sulfur com pounds therein and to improve the cetane number thereof, the improvement of (a) contacting the oil with acetonitrile to extract colored reaction products therein; and obtaining a raflinate phase predominating in said oil (b) washing the resulting raiiinate phase with water to remove any dissolved solvent; and

(c) drying the treated oil.

12. In the treatment of sour fuel oils of the diesel-fuel boiling range by contacting the oil at 040 C. with sufih cient nitrogen dioxide to react with the sulfur compounds therein and to improve the cetane number thereof, the improvement of V (a) contacting the oil with phenol to extract colored reaction products therein; and obtaining a rafiinate phase predominating in said oil; and

(b) washing the resulting raflinate phase with water to remove any dissolved solvent; and

(c) drying the treated oil.

13. In the treatment of sour fuel oils of the diesel-fuel boiling range by contacting the oil at 040 C. with suffi cient nitrogen dioxide to react with the sulfur compounds therein and to improve the cetane number thereof, the improvement of (a) contacting the oil with ethanolamine to extract colored reaction products therein; and obtaining a rafiinate phase predominating in said oil; and

(b) washing the resulting raffinate phase with Water to remove any dissolved solvent; and

(c) drying the treated oil.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Ephraim: Inorganic Chemistry, 5th edition, Interscience Publishers Inc., N.Y.C. (1949), pp. 715 and 716. Q.D. 151, E64ac, 1948c. V 

1. IN THE TREATMENT OF FUEL OILS OF THE DIESEL-FUEL BOILING RANGE BY CONTACTING THE OIL AT 0* -40*C. WITH SUFFICIENT NITROGEN DIOXIDE TO IMPROVE THE CETANE NUMBER THEREOF, THE IMPROVEMENT OF (A) CONTACTING THE TREATED OIL WITH A SOLVENT SELECTED FROM THE GROUP CONSISTING OF NITROMETHANE, DIMETHYLFORMAMIDE, PYRIDINE, ACETONITRILE, GLYCOLONITRILE, ETHYLENE GLYCOL, ETHANOLAMINE, AND PHENOL; AND OBTAINING A RAFFINATE PHASE PREDOMINATING IN SAID TREATED OIL AND (B) WASHING THE RESULTING RAFFINATE PHASE WITH WATER TO REMOVE ANY DISSOLVED SOLVENT. 